The correct option is D 750 g
Since the cake is being equally divided amongst the 3 brothers, so each brother is eating 13 of the cake.
If the weight of one piece is 250 grams, therefore, the weight of the entire cake would be three times the piece of one cake.
So, the total weight of the cake is
3×250 grams = 750 grams
The total weight of the cake is 750 grams.